High peak power waveguide junction circulators having inductive posts in each port for tuning circulator



Sept. 9, 1969 j JANSEN ET AL 3,466,571

HIGH PEAK POWER WAVEGUIDE JUNCTION CIRCULATORS HAVING INDUCTIVE POSTS IN EACH PORT FOR TUNING CIRCULATOR Filed Feb. 28. 1968 2 Sheets-Sheet 1 FIFTH PORT 24 CIRCULATORS SECOND PORT T 30 FOURTH THIRD l6 LATCH I 3 PORT PORT 26 LATCH FlRST 25 I I5 l4 SIXTH 20 PORT PORT V f RCVR FIG, 1 XMTR z-Ax|s r84 l7 CONTROL l a2 ERRITE) 80 s FT IRON (RUBBERGO 5 1 CEMENT) I euso T IRON) 1 i Fl& 3

CONTROL mvs/vrans JOSEPH mcuous JANSE/V 050 15 L. smaas v W FIG, 4 arromvers Se t. 9, 1969 J. N. JANSEN ETAL 3,466,571

HIGH PEAK POWER WAVEGUIDE JUNCTION CIRCULATORS HAVING INDUCTIVE POSTS IN EACH PORT FOR TUNING CIRCULATOR Filed Feb. 28, 1968 2 Sheets-Sheet 2 //VVENTOR$ JOSEPH NICHOLAS JANSE/V OSCAR L. STAGGS BY W ATTORNEYS United States Patent 3,466,571 HIGH PEAK POWER WAVEGUIDE JUNCTION CIR- CULATORS HAVING INDUCTIVE POSTS IN EACH PORT FOR TUNING CIRCULATOR Joseph Nicholas Jansen, Scottsdale, and Oscar L. Staggs, Phoenix, Ariz.,' assignors to Motorola, Inc., Franklin Park, 111., a corporation of Illinois Filed Feb. 28, 1968, Ser. No. 709,089 Int. Cl. I-I0lp 1/32 US. Cl. 333--1.1 12 Claims ABSTRACT OF THE DISCLOSURE A high peak power circulator having a ferrite post with a Z-axis perpendicular to the broad walls of the circulator junction. A pair of dielectric wafers are in intimate contact with the ends of the ferrite post and in turn are in intimate contact with a pair of susceptance platforms attached to the respective broad walls. Susceptance platforms present a lowered reactive impedance such that the electrical impedance of the junction is not optimum. For improving voltage breakdown characteristics, the susceptance platforms are thinner than required to tune the circulator in accordance with prior teachings. For tuning the circulator, each port communicating with the circulator junction has a pair of facing inductive posts on the respective sidewalls extending between the broad walls and disposed from the Z-axis of the ferrite about one-half wavelength of the desired frequency. The dielectric wafers extend outwardly over the ferrite posts for preventing corona discharge between the ferrite posts and the susceptance plates. A polymeric resin adhesive is disposed over each of the dielectric wafers. Two threeport circulators are constructed in a unitary base by separating the posts of two ports of the respective circulators by one-half wavelength of the desired frequency. The circulators are magnetically biased by a latching ferrite core for providing TR switch capabilities.

The subject matter disclosed and claimed herein was made under a Government contract with US. Army, Fort Monmouth, N. I.

Background of the invention This invention relates to microwave and RF type circulators and the switching systems utilizing such circulators and especially those having high peak power capabilities of simplified and low cost construction.

Peak power limitations in microwave and RF circulators are caused by arc-over and nonlinear power loss in a circulator ferrite post. The latter is a power limiting function due to the saturation of the ferrite. Arc-over is caused by corona breakdown and is determined by the waveguide junction geometry gas pressure Within the junction and types of material utilized. The limiting feature of the ferrite posts is caused by the parametric generation of first order spinwaves at the expense of the uniform precession mode of the magnetization vector and is a characteristic of the narrow resonance line Width ferrite materials selected for use in the circulator. By elongating the air gap between the waveguide susceptance plates, for a given RF peak power level, the RF magnetic field intensity can be reduced and therefore the nonlinear power loss threshold can be increased.

Among the factors causing corona breakdown are sharp corners within the junction, such as on the ferrite itself, and members adjacent the ferrite. Generally the ferrite post is sandwiched between a pair of dielectric wafers having a smaller diameter than the ferrite post. The prob- 3,466,571 Patented Sept. 9, 1969 lem in high peak power circulators has been a corona discharge between the ferrite post and the susceptance platforms between which the dielectric wafers are sandwiched. The purpose of making the dielectric wafers smaller in diameter or of smaller cross-section than the ferrite post is to broadband the circulator. The susceptance platforms have a thickness which impedance presented to the signals passing through the circulator. The thicker the susceptance plates, the greater the reactive impedance presented. The selection of thickness for the susceptance plates is usually performed empirically. In tuning a circulator to an optimum impedance, as later described, the susceptance platform reactive impedance, plus the combined impedances presented by the ferrite post and the dielectric wafers, tune the junction, hence the circulator, to an optimum impedance. An optimum impedance is defined as that impedance presented by the junction to an incoming signal which is as close as possible to the characteristic impedance of the Waveguide or other types of ports communicating with the junction. It is also desired to have what is termed a small grouping of impedances. This terminology is derived from utilization of the so-called Smith charts wherein the impedance variations with frequency over the desired bandwidth have small variations. The tighter the grouping, the better the impedance matching across of the junction and the circulator.

Any air gap or protrusion from any portion in the junction area can initiate arc-over at less than desired peak power levels. Practice to date in the X-band frequencies using the WR9O standard waveguide in the unpressurized condition, peak power in a three-port circulator has been limited to between 65 kw. and kw. This limitation usually has been imposed by corona breakdown.

Another factor in corona breakdown is the pressure of the gas inside the junction. In'rarified atmospheres, such as in high altitude operations, the tendency for corona breakdown is substantially increased. Corona breakdown threshold can be increased by pressurizing the inside of the waveguide. This can be expensive and requires additional equipment and therefore increases the cost of the system in which the circulator is being installed.

Also it is desired for conservation of power to use a so-called latching circulator. A latching circulator is one in which the magnetic bias is provided by a so-called permanent magnet which includes the ferrite post within its magnetic path. Ferrite magnets exhibiting rectangular hysteresis characteristics can be switched between two directions of remanent magnetization. By so switching the magnet, the operation of the circulator can be reversed because of the reversal of the magnetic field along the Z-axis of the ferrite post. In switching such ferrite magnets between opposite remanent magnetization states, high amplitude currents can be induced within the waveguide walls. Such induced currents, often referred to as eddy currents, increase the switching time of the permanent magnet. Eddy currents can be minimized without upsetting the peak power capability by judiciously cutting a waveguide slot at a place in the waveguide where RF fields are at a minimum.

Circulators can make very effective TR switches and especially between a plurality of antennae and a transmitter-receiver setup. Such switching systems can eliminate electromachanical switches and provide for very high speed switching, especially if latching types of circulators are used. It is also desired that the TR switch be minimized in size, dissipate a minimum amount of energy, be operable at extremely high altitude and at high temperatures. Peak powers of many transmitters greatly exceed the 100 kw. limit imposed in X-band circulators. It is therefore desired to have a circulator and a circulator switching sys tem capable of handling several times the 100 kw. limit imposed by the geometry of the X-band waveguide circulators.

Summary of the invention It is an object of the present invention to provide an improved, low cost, simple, compact high peak power circulator and circulatory switching system.

It is another object of the present invention to provide a circulator usable in the X-band having a peak power handling capability in excess of 200 kilowatts and when utilized in other frequency bands having correspondingly high peak power handling capabilities.

A feature of the present invention includes a combination of a circular cylindrical ferrite post centrally located in a junction of a circulator having a Z-axis perpendicular to the broad walls of the junction with a pair of dielectric wafers on opposing ends of the ferrite post and extending radially outwardly of the ferrite post. The wafers are in turn sandwiched between a pair of susceptance plates having a thickness less than that required to tune the circulator junction to an optimum impedance in the absence of a pair of inductive posts provided in each of the communicating ports and located approximately onehalf wavelength from the Z-axis of the ferrite material.

Another feature of the present invention is the provision of a polymeric resin adhesive spread around the ferrite post and covering the two wafers such as to make a smooth surface between the ferrite post and the adjacent suceptance platforms.

Another feature of the invention is the provision of two circulators, as described in the above features, formed in a unitary body with two of the ports communicating together and being spaced apart approximately one-half wavelength of the desired frequency of operation.

In accordance with the present invention a circulator is provided having a ferrite post with parallel fiat surfaces and formed in the shape of a circular cylinder and sandwiched between a pair of dielectric wafers which are in intimate contact respectively with the opposite surfaces. The wafers extend radially outwardly of the ferrite post. The wafers are in turn sandwiched between a pair of susceptance platforms and have a relationship between the ferrite post and the susceptance platforms tending to prevent corona breakdown therebetween. A polymeric resin adhesive is spread over the wafers such that a smooth transition is provided between the ferrite post and the susceptance platforms. In one version of the present invention a magnetic core in the shape of a yolk and exhibiting rectangular hysteresis characteristics is disposed to include the circulator junction ferrite post in its magnetic path. The core has a high degree of remanent magnetization such that it can successfully magnetically bias the ferrite post for optimum circulator operation. By switching the direction of remanent magnetization of the magnetic core, the circulator operation may be reversed such that differing ports may be interconnected for providing a selective switching system.

In one embodiment of the invention, two circulators are formed in a unitary body. Inductive posts on a selected port of each of the two circulators are a common waveguide and are spaced apart by one-half wavelength of the desired operating frequency. With this setup, a transmitter and receiver can be connected to one port in each of the two circulators with two antennae connected to the other two ports that are not connected together. By magnetically biasing ferrite posts in the circulators in a first direction, the transmitter is connected to one of the antennae for transmitting power thereto while the antenna-intercepted signals are returned to the receiver. By reversing the magnetic biasing, a second antenna receives signals from the transmitter and supplies signals to the receiver.

4 The drawing FIG. 1 is a simplified schematic diagram of a switching system utilizing circulators incorporating the teaching of the present invention. FIG. 2 is a diagrammatic perspective view of a two-circulator switching system having cut-away portions for illustrating the internal constructional features and usable as the two-circulator system shown in FIG. 1.

FIG. 3 is a diagrammatic sectional view of the FIG. 2 apparatus taken in the direction of the arrows along line 33 in FIG. 2.

FIG. 4 is a diagrammatic showing of a magnetic biasing circuit used to bias one oft he ferrite posts in the FIG. 2 apparatus.

Description of the illustrative embodiment Referring now more particularly to the drawing, like parts and structural features are indicated by like numerals in the various view and diagrams. Referring more particularly now to FIG. 1, there is shown a transmitter 10 and a receiver 11 designed to be selectively connected to a pair of antennae 12 and 13 through circulators 14 and 15. Latching control devices 16 and 17 are schematically shown as controlling the operation of the circulators as later described. The first circulator 14 has a first port 20 receiving signals from transmitter 10, a second port 21 connecting antenna 12 to the first circulator. A third port 22 connects the first circulator 14 to the fourth port 23 of second circulator 15. The second circulator has a fifth port 24 connected to antenna 13 and a sixth port 25 for supplying signal to receiver 11.

When the ferrite posts (not shown in FIG. 1) are magnetically biased along the Z-axis in a first direction, circulators 14 and 15 circulate signals in a first direction as indicated by arrows 26, 27 and 28. In the first direction, signals from transmitter 10 arriving through first port are communicated directly to second port 21 for emission by antenna 12. Signals intercepted by antenna 12 are supplied through second port 21, thence to sixth port and receiver 11 via third port 22 and fourth port 23. Arrows 27 and 28 indicate the latter operation. Signals intercepted by antenna 13 are supplied through fifth port 24, thence through fourth port 23, third port 22 to first port 20 wherein they are dissipated in transmitter 10.

By reversing the polarity of the remanent magnetization in the latch devices 16 and 17 (as later explained) the circular operation is reversed as indicated by dotted arrows 29, 30 and 31. In the latter case, signals from transmitter 10 arrive at the first circulator 14 through first port 20, thence are transmitted to the antenna 13 via third port 22, fourth port 23, and thence through fifth port 24, as indicated by arrows 29 and 30. Signals intercepted by antenna 13 are supplied by receiver 11 via fifth port 24 and sixth port 25 as indicated by arrow 31. Signals intercepted by antenna 12 are then supplied through second port 21, thence through first port 28 to transmitter 10 where they are dissipated.

The circulators 14 and 15 are embodied, in the apparatus shown in more detail in FIG. 2 which also illustrates several features of the present invention. The circulators 14 and 15 are formed in unitary base member which has a cover plate 36 therover for forming waveguides, later discussed. Cover plate 36 is cut away to show the various internal constructional features of the apparatus. The base and cover plate are usually constructed of aluminum or aluminum alloy. The waveguides formed within the base plate 35 in constituting the various ports and junctions of circulators, as will be elaborated upon, have a pair of facing broad walls 37 and 38. The sidewalls of the waveguides include sidewall 39 extending from first port 20 to third port 22, sidewall 40 extending from sixth port 25 to fifth port 24, sidewall 41 extending from fifth port 24 to second port 21, sidewall 42 extending from second port 21 through first port 20.

The two circulator junctions are. best understood by reference to FIGS. 2, 3 and 4. FIG. 3 includes a detailed showing of second circulator 15 Whereas FIG. 4 diagrammatically shows a magnetic circuit and the various parts of first circulator 14. Second circulator 15 has a junction common to the fourth, fifth and sixth ports which includes a pair of spaced-apart and facing susceptance platforms 50 and 51 centrally located in the junction area. Susceptance plates 50, 51 are triangularly shaped with the apex of the angles being symmetrically disposed in the various ports. For a four-port or other multi-port circulator, other shapes of susceptance plates may be used. In a similar manner, the susceptance plates 52 and '53 are formed and disposed in a junction area of first circulator 14. These susceptance platforms are an important portion of the present invention and will be discussed later in detail. The circulator junctions include ferrite posts 54 and 55 formed of gyromagnetic material. The ferrite posts 54, 55 are respectively sandwiched between pairs of dielectric wafers 56, 57 and 63, 64. Each of the wafers extend radially outwardly, as at 58 and 59 (FIG. 3) of the circular shaped ferrite post cylinders. The junction construction inside the junction area is completed by polymeric resin adhesive 60' such as a rubber cement, disposed circumferentially of all of the dielectric wafers. I According to this invention, the susceptance platforms have a thickness less than that normally used, as will be described, for increasng the spacing therebetween as best seen in FIG. 3. This of course increases the maximum voltage in any RF field which may be imposed on the junction. Further, the dielectric wafers sandwiching the ferrite posts extending radially outwardly of the ferrite posts, form a corona barrier between the ferrite posts and the susceptance platforms. Even at that, the sharp corners of the dielectric wafers could have a tendency to initiate corona breakdown because of the tendency of RF fields to concentrate at sharp points. To eliminate this possibility a polymeric resin adhesive is carefully applied around the assembly as best seen in FIG. 3 to provide smooth transition surfaces between the ferrite posts and the susceptance platforms. To illustrate how carefully this must be done, an air void formed in the adhesive of 0.0001 inch diameter was sufiicient to cause a corona discharge at high power RF fields. For this reason epoxy adhesives to date have not been found suitable. It is preferred to have a slow setting resin adhesive such as one that requires about two hours to harden. Care must be exercised in assembling the junction such that no air gaps are provided. For this reason surfaces 61 and 62 of ferrite post 54 should be accurately parallel to each other and perpendicular to the Z-axis of the ferrite post. Dielectric wafers 56 and 57 should be of the cold flowing type such that any imperfections in the surface of 61 and 62 are filled by the material forming the wafers. It is understood, of course, that the entire assembly is under compression to force the dielectric wafer material into the ferrite imperfections as well as the imperfections on the soft iron pole pieces 80 and -81. In any event air gaps should be avoided. Without air gaps the susceptance platforms 51 and 50 and the wafers 56 and 57 as well as post 54 are said to be in intimate contact one with the other.

In selecting the material for dielectric wafers 56 and 57 a thermoplastic should not be chosen if the device is to be operated at high environmental temperatures. Cold flowing would be too great and could detune the circulator junction. Also the wafers should have a relatively low dielectric constant. Typical low dielectric constants are 2.1 to 2.5. The extension of wafers 56 and 57 radially outwardly of the ferrite post 54 need not be very great. For example, success has been obtained by extending the wafers out about 0.010 inch. If the wafer is left flush with the cylindrical sides of ferrite post 54 then there is still provided a short path between post 54 and susceptance platforms 50 and 51 which can permit corona breakdown at a lower peak power.

Tuning a circular junction including impedance matching of the port to the circulator junction includes all variations such as the waveguide size, the ferrite post, the dielectric wafers, the susceptance platforms, plus physical geometry and electrical properties of all components. Because of the complex tuning function, tuning is done empirically. In the X-band the distance or spacing between the 0.900 inch wide broad walls is 0.400 inch with a ferrite post having a diameter of about 0.275 inch and susceptance plates with a side dimension of somewhat greater than one inch. The susceptance platforms have a thickness of about inch to tune or impedance match the junction to the three ports. Spacing between the susceptance platforms is 0.276 inch. By halving the thickness of the susceptance platforms the spacing is increased to 0.338 inch which greatly increases the corona breakdown characteristic of the junction. Such a reduced thickness greatly detunes the junction effectively making it inoperative. To retune the circulator to the desired frequency, facing pairs of inductive posts 70-75 are placed in each of the respective ports (FIG. 2) about one-half wave length from the Z-axis of the ferrite posts 54 and 55. The inductive posts extend between the broad walls of the respective waveguides along the respective side walls. To prevent corona discharge, each port has a substantial thickness along the waveguide length and rounded corners, as shown. The greater the distance the inductive posts extend into the waveguide or port the greater the provided inductance. Again the tuning of the circulator is done empirically with the distance the inductive posts extend into the waveguides being determined by cut and try methods. It is important to have the inductive post about one-half wavelength from the Z-axis since this is a voltage node, wherein, minimum voltage is experienced. It has been found that with inductive posts 70 through 75 and thinned susceptance platforms 50, 51, 52 and 53 that broad banding of the circulator is accomplished with higher peak power than that provided by the above described prior art circulators. For example, peak powers in excess of 200 kilowatts were obtained by practicing the invention.

A secondary improvement in making these susceptance platforms 50 throhgh 53 of reduced thickness is that the volume of ferrite material in the ferrite posts 54 and 55 is increased in that the posts are longer in axial direction. This increased volume of material tends to reduce nonlinear losses in the ferrite posts. It also increases its peak power handling capability; the maximum benefit remains in the improvement in the corona breakdown characteristics of the circulators.

Referring next to FIG. 4, the magnetic biasing devices 16 and 17 are described. Device 16 is shown in diagrammatic form with like numbers denoting like parts in FIG. 3 in second circulator 15. Ferrite post 55 is sandwiched between spaced-apart dielectric washers 63 and 64 which are in turn sandwiched between susceptance platforms 52 and 53. Soft iron pole pieces and 81 are each disposed in an aperture formed in the respective susceptance platforms and are pressed against the dielectric wafers. A C-shaped ferrite core 82 firmly'engages the low reluctance pole pieces 80 and 81 to complete a low reluctance magnetic circuit. C-shaped core 82 is formed of ferromagnetic material having a good rectangular hysteresis characteristic, that is, the remanent magnetization is a high percentage of the saturation magnetization. The remanent magnetization must be suflicient to magnetically bias ferrite post 55 to effect circulator operation. For example, ferro-magnetic material having a coercive force of about 15 gauss and a remanent magnetization, B of 2000 gauss was sucessfully used to latch a circulator using the present invention. Design approaches can alter these C-core characteristics. In addition, each core 82 should have high coercive force and a high curie temperature such as found in lithium-nickel ferrite. Ferrite post 55 may be formed of gadolinium-doped ittrium-ferric garnet.

The direction of remanent magnetization in core 82 and therefore the direction of magnetic biasing along the Z- axis of post 55 is selectively reversed by current flowing through coil 83 from control circuit 84. By causing a current to flow in a first direction through coil 83, core 82 is switched to a first remanent magnetic state which biases the ferrite posts to cause the first mode of operation in the circulators, illustrated by arrows 26, 27 and 28. By reversing the current, and therefore the direction of magnetic bias, a second mode of operation, indicated by arrows 29, 30 and 31, is accomplished. Control 84 may be any electronic selective control circuit, the construction of which is not pertinent to practice of this invention and therefore will not be described. Control 84 may be made to simultaneously switch latch devices 16 and 17.

In switching the core 82, eddy currents are induced in the cover and base and 36 of the circulator structures. Such eddy currents take energy from the switching by inducing opposing fields which cause the switching action of the core 82 to slow. To eliminate eddy currents, eddy current slots are milled or otherwise cut into base 35 as at 90 and 91. The slots are cut from the outside of the housing to the Z-axis. The slots will then be filled with epoxy cement to permit pressurization of the waveguide, if desired, and to provide dielectric insulation. The illustrated slots are cut at an angle of between the first port 20 and second port 21 of first circulator 14 and between fifth port 24 and sixth port 25 of second circulator 15. At these points the RF electric field intensity is at a theoretical minimum to make RF power loss negligible. With the eddy current slots in the waveguide structure, as shown, the corona breakdown was unaffected, at least is up to 210 kilowatts in laboratory experiments and the switching time of core 82 was less than 300 microseconds. With a silver plating over the epoxy filled slot, switching time was increased to 500 microseconds. Switching time can be further reduced by increasing the voltage across winding 83. The slots in the above described experiments had a thickness of 0.012 inch.

In one test of the illustrative embodiment, peak power of 210 killowatts was successfully passed through an unpressurized waveguide. At a reduced pressure equivalent to an altitude of 23,000 feet and an environmental temperature of 85 C., a peak power of killowatts was obtained. With pressurizing, of course, the peak power of the circulator would be greatly enhanced. The exact upper power limit of a constructed illustrative embodiment has not been accurately determined at this time. The above described peak powers are about twice that expected from an X-band waveguide circulator. The standing wave ratio was less than 1.14 to l with good isolation between the various ports.

We claim:

1. A high peak-power multiport waveguide circulator for operating at a desired frequency and having a common junction for all the ports with a pair of spaced-apart facing broad walls in the junction and a gyromagnetic ferrite post disposed between said broad walls with a Z-axis perpendicular to said broad walls and having a pair of substantially parallel surfaces respectively facing said broad walls,

the improvement including in combination,

a pair of low dielectric-constant dielectric wafers respectively in intimate contact with said surfaces of the ferrite post with said dielectric wafers everywhere outwardly extending beyond said ferrite post into the junction,

a susceptance platform on each of said broad walls and each having a thickness extending into said junction a distance less than that required to provide a reactive impedance for tuning with said wafers and ferrite post and the other susceptance platform in said junction to an optimum impedance at said desired frequency, the provided reactive impedance tuning said junction to an impedance other than said optimum impedance,

said'susceptance platforms being in respective intimate contact with said dielectric wafers,

each of said ports including a waveguide portion contiguous with said junction, each having a pair of facing broad walls and a pair of facing side walls,

a pair of facing inductive posts in each waveguide portion extending between said broad walls along said side walls, respectively, and disposed from said Z- axis about one-half wavelength of the desired frequency as measured within said waveguide portions, said posts being constructed to provide an inductance in the respective ports for tuning the circulator to said desired frequency with said susceptance platform reactive impedance, and means to bias said ferrite post along the Z-axis.

2. The circulator of claim 1 further including a dielectric fillet extending round each of said dielectric wafers for forming a smooth surface transition from said ferrite post to said junction broad walls, respectively.

3. The circulator of claim 2 wherein each fillet consists of a slow-setting polymeric resin type of adhesive having no air bubbles therein with a smooth outer surface.

4. The circulator of claim 1 wherein said ferrite post has a circular cylindrical shape and said parallel surfaces are perpendicular to said Z-axis, and

said susceptance platforms each having a thickness not greater than one-half of the thickness required to tune said circulator to said desired frequency in the absence of said inductive posts.

5. The circulator of claim 4 wherein said means to magnetically bias said ferrite post includes a pair of low reluctance pole pieces in intimate Contact With Said dielectric wafers, respectively,

said susceptance platforms having apertures through which said pole pieces respectively extend,

a C-core of magnetic material exhibiting a rectangular hysteresis characteristic with a remanent magnetization sufficient to supply a magnetic bias to said ferrite post, said C-core being switchable between opposite directions of remanent magnetization.

6. The circulator of claim 5 wherein said C-core extends to said wafers symmetrically between two adjacent ports, said circulator having a slot extending from said Z-axis to its outer extremity symmetrically between said two adjacent ports for reducing eddy currents in said circulator.

7. The circulator of claim 6 wherein an epoxy material fills said slot.

8. The circulator of claim 6 wherein said Ccore has lithium-nickel ferrite material.

9. A microwave switching system of the circulator type for operating at a desired frequency having a given wavelentgh in a waveguide including in combination,

first and second circulator means, first, second and third waveguide ports in said first circulator means, fourth, fifth and sixth waveguide ports in said second circulator means, each circulator means having a common junction contiguous with said waveguide ports, respectively,

two facing broad walls continuously extending through all said waveguide ports and junctions,

first and second gyromagnetic ferrite posts each having a Z-axis extending perpendicular to said broad walls with oppositely facing surfaces parallel to said broad walls and being respectively disposed centrally in said junctions of said first and second circulator means,

a pair of low-dielectric-constant dielectric wafers adjacent each ferrite post and respectively in intimate contact with said oppositely facing surfaces thereof and said dielectric wafers everywhere extending radially beyond the respective ferrite posts into the respective junctions,

a pair of facing spaced-apart susceptance platforms in each junction disposed symmetrically of said ferrite posts, respectively, said susceptance platforms in each pair being on the said broad walls, respectively, :and each susceptance platform extending into the respective junctions a distance less than that required to provide a reactive impedance for tuning with said wafers, ferrite post and the other susceptance platform in the junction, the respective circulator means to an optimum impedance at said desired frequency, the susceptance platform provided reactive'impedance being sufliciently large to tune the respective circular means to an impedance other than said optimum impedance,

each susceptance platform being respectively in intimate contact with said dielectric wafers,

each of said waveguide ports having a pair of facing and spaced-apart inductive posts extending between said broad walls and disposed from the respective Z-axes about one-half said given wavelength, said posts in each circulator means exhibiting an inductance tuning the respective circulator means to said optimum impedance,

a waveguide section joining said third and fourth ports with a distance between said inductive postsin said third and fourth ports of about one-half said given wavelength,

circulator bias means in each circulator means for respectively biasing said ferrite posts along the Z-axis and switchable between first and second magnetic directions such that when said ferrite posts are biased in said first direction said first port supplies signals to said second port, said second port supplies signals to said fourth port through said third port, said fourth port supplies signals to said sixth port and when said ferrite posts are magnetically biased in said second direction said first port supplies signals to said fifth port through said third port and said fourth port and said fifth port supplies signals to said sixth port.

10. The system of claim 9 wherein a unitary metal member has one of said broad walls, on said side walls and a second metal member forms said second broad walls,

said unitary metal member having a pair of slots extending from the respective Z-axes outwardly and symmetrically between said first and second ports and said fifth and sixth ports, respectively. 11. The system of claim 10 wherein epoxy material fills said slots flush with said one broad wall and further including a fillet of polymeric resin adhesive around each dielectric wafer forming a smooth surface between said ferrite posts and said susceptance plat-forms.

12. The system of claim 9 wherein said circulator bias means includes a pair of C-cores having magnetic material exhibiting rectangular hysteresis characteristics with a remanent magnetization suificient to supply .a magnetic bias respectively to said ferrite posts and having opposing facing surfaces opposite said respective ferrite posts,

said susceptance platforms each having an aperture co- .axial with the respective ferrite posts,

low reluctance pole pieces extending respectively from and in intimate contact with respective ones of said dielectric wafers through said apertures to contact said respective C-cores for completing a magnetic for each C-core, and

means for selectively switching the remanent magnetization of said C-cores for supplying said first and second directions of magnetic bias.

References Cited UNITED STATES PATENTS 3,104,361 9/1963 Leetmaa et al. 333l.1 3,316,505 4/1967 Geiszler 333--1.1 3,324,418 6/1967 Caswell 3331.1

HERMAN KARL SAALBACH, Primary Examiner PAUL L. GENSLER, Assistant Examiner US. Cl. X.R. 33313; 343-853 

